Balanced folder assembly

ABSTRACT

An improved sheet-folding apparatus includes a folder blade which is reciprocated by operation of a first crank assembly to move sheets into a nip formed by a pair of folder rollers. A second crank assembly is connected to a crankshaft for operating the first crank assembly. This second crank assembly is operable to maintain the torque load applied to the crankshaft substantially constant by applying to the crankshaft a fluctuating torque load which offsets a fluctuating torque load applied to the crankshaft by the first crank assembly.

United States Patent 1111 3,

[72] Inventor Charles H. Dufour [56] References Cited Westerly UNITED STATES PATENTS g QE A- x 1969 907,121 12/1908 Bray 270/83 E f 5 2,619,839 12/1952 Love 74/603 9 [73] Assignee Harrls-lntertype Corporation Primary Examiner-Robert W. Michell Cleveland, Ohio Assistant ExaminerR. P. Dyer Att0rneyYount and Tarolli [54] BALANCED FOLDER ASSEMBLY 13 Claims, 13 Drawing Figs. ABSTRACT: An improved sheet-folding apparatus includes a folder blade which is reciprocated by operation of a first crank (gl B65 assembly to move sheets into a p formed y a p of folder [501 Fieid 270/83 84 rollers. A second crank assembly is connected to a crankshaft for operating the first crank assembly. This second crank as- 74/603 sembly is operable to maintain the torque load applied to the crankshaft substantially constant by applying to the crankshaft a fluctuating torque load which offsets a fluctuating torque load applied to the crankshaft by the first crank assembly.

PATENTED JAN 4:912

SHEET 2 BF 4 FIGS awavroe CHARLES 1 DUFOUR ATTORNEYS PATENTEU JAN 4 I972 SHEET 3 [1F 4 ATTORNEYS BALANCED FOLDER ASSEMBLY This invention relates generally to a sheet-handling apparatus and more particularly to an apparatus for folding sheets.

A known sheet folder of the knifeor chopper-type folds sheets by passing them through a nip fonned by a pair of cooperating rollers or cylinders. A blade or knife is moved downwardly into engagement with the sheets and forces them into the nip. The blade is then withdrawn upwardly. The blade is reciprocated through these down and up operating strokes by operation of a crank assembly.

The reciprocative movement of the blade produces torque fluctuations in the load applied to the crank assembly and thus on the folder drive train. Torque fluctuations on the drive train tend to vibrate the folder assembly and a printing press associated with the folder assembly. This vibration tends to adversely effect the operation of mechanical components of the folder and printing press.

Accordingly, it is an object of this invention to provide a new and improved sheet-handling apparatus wherein a substantially constant torque load is applied to a drive train for a reciprocating mass system.

Another object of this invention is to provide a new and improved statically and dynamically balanced sheet folder apparatus having a blade which is reciprocated to efiect a folding of the sheets.

Another object of this invention is to provide a new and improved sheet folder apparatus having a blade which is reciprocated to move sheets into the nip of a pair of folder rollers and a counterweight means for offsetting torque fluctuations resulting from reciprocation of the blade.

Another object of this invention is to provide a new and improved sheet folder apparatus having a first crank assembly for reciprocating a blade to move sheets into the nip of a pair of folder rollers and a second crank assembly for offsetting torque fluctuations resulting from reciprocation of the blade.

These and other objects and features of the invention will become more apparent upon a consideration of the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of a knife-type folder construction in accordance with the present invention;

FIG. 2 is a schematic elevational view, taken generally along the line 22 of FIG. 1, illustrating the relationship between a chopper or knife assembly and a folder crank assembly for operating the knife assembly;

FIG. 3 is a schematic illustration, taken generally along the line 3-3 of FIG. 2, illustrating the relationship between the folder crank assembly of FIG. 2, a crankshaft, a crankshaft drive train, and a counterweight crank assembly of the folder of FIG. 1;

FIG. 4 is a schematic illustration, taken generally along the line 4-4 of FIG. 3, further illustrating the counterweight crank assembly;

FIG. 5 is a schematic illustration, taken generally along the line 5-5 of FIG. 4, illustrating the relationship of the counterweight crank assembly to a mounting or support bracket;

FIGS. 6-9 are graphic illustrations approximating variations in velocity, acceleration, torque arm, and load torque, respectively, for the folder crank assembly during operation of the folder of FIG. I; and

FIGS. 10-13 are graphic illustrations approximating variations in velocity, acceleration, torque arm, and load torque, respectively, for the counterweight crank assembly during operation of the folder of FIG. 1.

Although it is contemplated that the present invention will be used in many different types of sheet-handling devices, such as packers and folders, it is disclosed herein in a knifeor chopper"-type folder. A knife-type folder constructed in accordance with the present invention includes a pair of folder rollers or cylinders and a blade which is reciprocated to move sheets into a nip defined by these rollers. A counterweight assembly is provided for offsetting torque fluctuations resulting from reciprocation of the blade. This counterweight assembly can take many different forms including that of a crank assembly which reciprocates a mass in an out-of-phase relationship with reciprocative movement of the blade.

A knifeor chopper-type folder 20 forming a specific preferred embodiment of the invention as illustrated in FIGS. 1 and 2. The folder 20 includes a pair of folder rollers or cylinders 22 and 24 which cooperate to define a nip 26 through which sheets of material 30 pass either singularly or in groups or gathers. As the sheets 30 pass through the nip 26 a fold is formed along a predetermined fold line. The blade 34 is moved from a raised position (shown in dashed lines in FIG. 2) to a lowered position (shown in solid lines in FIG. 2) to press the sheets into the nip 26. The blade 34 is reciprocated between the raised and lowered positions by means of a folder crank assembly 36 which is driven by a crankshaft 38.

The reciprocation of the blade 34 under the influence of the crank assembly 36 results in the crank assembly applying a fluctuating or uneven torque load to the crankshafi 38. Since the crankshaft 38 and folder rollers 22 and 24 are driven by common drive train, a part of which is indicated at 42 in FIG. 1, the fluctuating torque load tends to cause the folder rollers 22 and 24 to be driven at varying speeds by the drive train. In addition, the fluctuating torque load on the crankshaft 38 results in the folder drive train being vibrated or shaken while it is being operated thereby causing variations in perforations in the sheets, cut off of the sheets, and folds.

A counterweight assembly 46 is connected to the crankshaft 38 (see FIGS. 3 and 4) to maintain the torque load on the crankshaft 38 substantially constant. Accordingly, the counterweight assembly 46 applies to the crankshaft 38 a fluctuating torque load which is equal and opposite to the torque load applied to the crankshaft 38 by the crank assembly 36. In the illustrated embodiment of the invention, the counterweight assembly 46 includes a crank assembly 50 which is operated by rotation of the crankshaft 38 to reciprocate a mass or arm 52. The arm 52 is reciprocated with the same frequency and out of phase, in either a leading or lagging sense, with the reciprocation of the blade 34. The mass and rotational inertia of the counterweight assembly 46 is such that the torque load applied to the crankshaft 38 by the crank assembly 50 is equal and opposite to the torque load applied to the crankshaft 38 by the crank assembly 36. Therefore, the combined torque load on the crankshaft 38 is substantially constant.

During operation of the folder assembly 20, sheets 30 are fed either one at a time or in groups to a folder station 56 by rotation of a plurality of feed rollers 58 through 68 (FIG. I). The forward movement of the sheets is arrested by engagement with a stop member 72 while the sheets are supported on a plate 74 overlying the folder rollers 22 and 24. The sheets are retained in place with their leading end portions engaging the stop 72 by suitable brushes 78 which function in a known manner to prevent the sheets from jumping back."

During this positioning of the sheets at the folder station 56, the crank assembly 36 maintains the blade 34 in a position above the support plate 74 by pivoting the blade arm 82 upwardly about a support shaft 84 (see the dash line position of FIG. 2). Once the sheets 30 are positioned at the folder station 56 by engagement with the stop member 72, the crank assembly 36 moves the blade 34 downwardly so that it engages the sheets 30 along a predetermined fold line and presses the sheets through a slot 86 in the support plate 74 and into the nip 26 between the rollers 22 and 24. The rollers 22 and 24 are rotated continuously in the direction indicated by the arrows in FIG. 2 and engage the sheets to move them downwardly while folding them along the predetermined fold line. As the sheets are being folded by the rollers 22 and 24, the crank assembly 36 pivots the arm 82 upwardly to move the blade 34 out of engagement with the sheets 30 and enable the next group of sheets to enter the fold station 56. Although the movement of the blade 34 has been described as including two separate strokes, that is a downward stroke and an upward stroke, it should be understood that the crankshaft 38 is continuously rotating so that the crank assembly 36 is continuously reciprocating the blade between the raised and lowered positions to enable sheets to be quickly folded by the folder 20.

The crank assembly 36 includes a wheel member 88 which is rotated at a substantially constant speed by the crankshaft 38 during operation of the folder assembly 20. A crank link 90 is pivotally connected to the crank wheel 88 at a pivot connection 92. The opposite end portion of the link 90 is pivotally connected at 94 to the blade arm 82. Of course, rotation of the crank wheel 88 raises and lowers the pivot connection 92 to reciprocate the arm 82 and blade 34 about the support shaft "84 to thereby raise and lower the blade. This reciprocative movement of the blade 34 and arm 82 results in their downward movement being arrested when the pivot connection 92 is adjacent a point designated 90 in FIG. 2. The blade is then moved upwardly until the pivot connection 92 is adjacent the point designated 270 in FIG. 2. The upward movement is then arrested and the next downward stroke initiated.

This reciprocative movement of the blade 34 and arm 82 applies a fluctuating torque load to the crankshaft 38. This fluctuating torque load is ofiset by the counterweight assembly 46. The crank assembly 50 of the counterweight assembly 46 includes a crank wheel or member 100 which is fixedly connected to the crankshaft 38 (see FIG. 4). The crank wheel 100 is connected with the mass or arm 52 by a connector link 102 which is pivotally connected at 104 to the crank wheel and at 106 to the arm 52. The opposite end portion of the arm 52 is pivotally connected at 110 to a support or mounting bracket 112 (see FIG. 5). The mounting bracket 112 is connected to a frame 114 of the folder assembly 20.

The drive train 42 rotates the crankshaft 38 to operate the crank assemblies 36 and 50. The drive train 42 includes a gear 118 (see FIG. 1) which is fixedly connected to the crankshaft 38. The crankshaft 38 is supported for rotation by a bracket 120 (FIG. 3) which is connected to the frame 114. The gear 118 is driven by a gear 122 of a gear train which also drives the folder rollers 22 and 24. Since the counterweight assembly 46 balances the fluctuating torque load applied to the crankshaft 38 by the crank assembly 36, the load on the drive train 42 is maintained substantially constant so that the drive train is operated in a smooth manner without undue jerking to thereby tend to minimize vibration of the folder and a printing press associated with the folder.

Simplified operating characteristics for the crank assembly 36 and blade arm 82 are illustrated graphically in FIGS. 6 through 9. Thus as the blade 34 is moved downwardly, the velocity of the blade reaches a maximum when the pivot connection 92 is approximately adjacent the point indicated at 0 in FIG. 2. As the downward movement of the blade 34 continues, the velocity is decreased until the blade 34 reaches its lowermost position and the pivot connection 92 is approximately adjacent the point designated 90. The direction of movement of the blade is then reversed and the velocity in the upward direction increased until the pivot connection 92 passes the point approximately indicated at I80 in FIG. 2. The upward velocity of the blade is then decreased until the pivot connection 92 reaches the point designated 270 when the blade 34 again begins to move downwardly. Thus, the velocity of the blade 34 varies in a manner which is approximated by the sinusoidal curve 130 in FIG. 6.

To provide the sinusoidally varying velocity illustrated in FIG. 6, the acceleration of the blade 34 must vary in a sinusoidal manner approximated by the curve 134 in. FIG. 7. It should be noted that the acceleration of the blade 34 is substantially zero when the blade is experiencing its maximum velocity and the pivot connection 92 is approximately adjacent either the joint indicated at 0 or at 180 in FIG. 2. Similarly, the blade 34 is subjected to its maximum acceleration when the pivot connection 92 is approximately adjacent to either the 90 or 270 designation of FIG. 2.

Since the extent to which the pivot connection 92 is located sidewardly of the center of the crankshaft 38 varies in a sinusoidal manner as the crankwheel 88 is rotated, the lever or torque arm for moving the blade 34 and blade arm 82 varies in a sinusoidal manner as approximated by the curve 136 of FIG. 8. It should be noted that the torque or lever arm is a maximum when the pivot connection 92 is adjacent to either the 0 or 180 designation of FIG. 2. It should also be noted that the torque or lever arm is substantially zero when the pivot connection 92 adjacent to either the or 270 designation.

The torque load applied by the crank assembly 36 to the crankshaft 38 fluctuates relative to a predetermined torque load (designated X in FIG. 9) in the manner approximated by the curve 140. A simplified explanation of the torque load is that it is the product of the torque arm (FIG. 8) the acceleration (FIG. 7) and the mass being accelerated. If the mass of the sheets 30 is ignored, the mass being accelerated remains substantially constant. Therefore, the torque load (FIG. 9) applied to the crankshaft 38 varies as a direct function of variations in the product of the torque arm and acceleration. Thus, there will be substantially zero variable torque load when either the value of the torque arm (FIG. 8) or the value of the acceleration (FIG. 7) is zero.

The velocity, acceleration, torque or lever arm and torque load characteristics for the counterweight assembly 46 are graphically illustrated in FIGS. 10 through 13. It should be noted that the characteristics for the counterweight assembly 46 are 90 out of phase with the corresponding characteristics for the crank assembly 36, blade arm 82 and blade 34. Thus, the velocity (FIG. 10) of the pivot connection 106 of the crank assembly 50 is zero when the pivot connection 104 is adjacent to the 0 designation of FIG. 4. The pivot connection 92 (FIG. 2) is offset 180 from the pivot connection 104 (FIG. 4). Therefore, when the pivot connection 104 is adjacent to the 0 designation of FIG. 4 which has the same location relative to the frame 114 as does the 180 designation of FIG. 2, the pivot connection 92 is adjacent to the point indicated 0 in FIG. 2 and knife blade 34 is being moved downwardly with its maximum velocity. Continued rotation of the crankshaft 38 through 90 of movement moves the pivot connection 104 ad jacent to the 90 designation of FIG. 4 and the pivot connection 106 is moving at its maximum velocity (FIG. 10). This 90 of rotation of the crankshaft 38 moves the pivot connection 92 (FIG. 2) adjacent to the 90 designation and the blade 34 is being moved with substantially zero instantaneous velocity. Thus, it can be seen that the velocity curve for the knife blade 34 is 90 out of phase with the velocity curve 144 for the pivot connection 106 of the counterweight crank assembly 50.

Variations in the acceleration of the pivot connection 106 are illustrated graphically by the curve 148 in FIG. 11. It should be noted that the pivot connection 106 is subjected to maximum rate of acceleration when the pivot connection 104 is adjacent to either the point designated 0 or 180 in FIG. 4. Thus, the acceleration curve 148 is 90 out of phase with the acceleration curve 134 for the blade 34. Therefore, the blade 34 is subjected to its maximum acceleration when the pivot connection 106 is being subjected to substantially zero acceleration. Similarly, when the pivot connection 106 is being subjected to its maximum acceleration, the blade 34 is being subjected to substantially zero acceleration.

The torque or lever arm for the connection 106 relative to the crankshaft 38 varies in a sinusoidal manner approximated by curve 150 in FIG. 12. It should be noted that the curve 150 is 90 out of phase with the torque or lever arm curve I36 of FIG. 8.

Since the mass of the counterweight assembly 46 remains constant, the torque load which is applied to the crankshaft 38 fluctuates in accordance with fluctuations in the product of the torque arm (FIG. 12) and acceleration of the mass (FIG. 11). Variations in this product are approximated by the torque load curve 154 in FIG. 13. It should be noted that the torque load curve 154 is 90 out of phase with the torque load curve approximately the fluctuations in the torque load applied to the crankshaft 38 by the crank assembly 36. The maximum and minimum torque illustrated graphically by the curves 140 and 154 are substantially equal. Therefore, the fluctuations in the torque load applied to the crankshaft 38 by the crank assembly 36 are effectively cancelled by the equal and opposite fluctuations in the torque load applied to the crankshaft 38 by the crank assembly 46. This is illustrated in FIGS. 9 and 13 wherein the torque load curve 140 and 154 are 90 out of phase and have equal and opposite magnitudes at any given time.

As will no doubt be understood by those skilled in the art the foregoing is a simplified explanation of the operation of crank assembly 36 and counterweight assembly 46. Also, the curves of FIGS. 6-13 represent only simplified approximations of the operating characteristics. These operating characteristics will vary somewhat from the simplified graphs of FIGS. 6-13 due to weight and rotational inertia effects which are present in the actual crank and counterweight assemblies. While the graphic illustrations of FIGS. 6-13 only approximate the operating characteristics which they depict, it is believed that they are sufiiciently informative since the depicted operating characteristics will vary between embodiments of the invention which differ only slightly from each other. It should also be understood that the indications of the 0, 90, 180 and 270 positions in FIGS. 2 and 4 of the drawings are only approximate and are not exactly located.

In view of the foregoing remarks, it can be seen that the sheet-folder assembly 20 includes a crank assembly 36 which is driven by a crankshaft 38 to reciprocate a folder blade 35 and move sheets into the nip 26 defined by the folder rollers 22 and 24. The fluctuating torque load which is applied to the crankshaft 38 by the crank assembly 36 as a result of this reciprocation of the blade 34 is offset by a fluctuating torque load which is applied to the crankshaft 38 by the counterweight assembly 46. In the illustrated embodiment of the invention, the counterweight assembly 46 includes a crank assembly 50 which is operable to pivot a mass, i.e., the arm 52, if a 90 out of phase relationship with the pivotal movement of the blade arm 82 by the crank assembly 36. This out of phase relationship between the arms 52 and 82 results in the fluctuating torque loads (see FIGS. 9 and 13) offsetting each other to maintain the torque load on the crankshaft 38 substantially constant.

In addition to dynamically balancing the fluctuating torque load applied to the crank shaft 38 by the crank assembly 36, the counterweight assembly 46 balances the static load applied to the crankshaft 38 by the crank assembly 36. This static balancing results from the 180 offset relationship between the pivot connection 92 to the crank wheel 88 of the crank assembly 36 and the pivot connection 104 to the crank wheel 100 of the crank assembly 50. Therefore, the static loads applied to the crankshaft 38 by the two crank assemblies 36 and 50 are located on opposite sides of the centerline of the crankshaft 38 and tend to balance each other. The static load applied to the crank wheel 100 of the pivot connection 104 can be adjusted to equal the load applied to the crank wheel 88 by means of a suitable counterweight 160 (see FIG. 4) which is connected to the arm 102. Thus, the counterweight assembly 46 both statically and dynamically balances the load applied to the crankshaft 38 by the crank assembly 36.

Although a specific preferred embodiment of the counterweight assembly 46 has been illustrated herein, it is contemplated that other specific embodiments of the counterweight assembly could be utilized. For example the pivot connection 110 (FIG. 4) could be located below the center of the crankshaft 38 or on the opposite side of the crankshaft. In addition, it is contemplated that various spring arrangements would be substituted for the illustrated counterweight assembly. It is also contemplated that the counterweight assembly 46 could be used in conjunction with other types of mechanisms, such as packers.

Having described a specific preferred embodiment of the invention, the following is claimed:

1. A sheet-folding apparatus comprising a pair of folder rollers cooperating to fonn a nip, means for positioning sheets in a predetermined relationship with said folder rollers, blade means for engaging the sheets and moving them into the nip formed by said folder rollers, means for reciprocating said blade means including a shah operatively connected with said blade means and drive means for rotating said shaft to effect reciprocation of said blade means, and counterweight means for offsetting torque fluctuation resulting from reciprocation of said blade means, said counterweight means being operatively connected with said shaft whereby rotation of said shaft operates said counterweight means to effect the offsetting of the torque fluctuations resulting from reciprocation of said blade means to thereby tend to minimize torque loading on said shaft during operation of said folding apparatus.

2. A sheet-folding apparatus as set forth in claim 1 wherein said counterweight means includes a mass which is operatively connected with said shaft and is reciprocated approximately out of phase with reciprocation of said blade means upon rotation of said shaft by said drive means.

3. A sheet-folding apparatus as set forth in claim 1 wherein said blade means includes a first pivotally mounted arm and a folder blade mounted on said first arm, said means for reciprocating said blade means includes a first crank assembly operatively connected with said shaft and said first arm for reciprocating said first arm to move said folder blade relative to said folder rollers, and said counterweight means includes a second pivotally mounted arm and a second crank assembly operatively connected with said shaft and said second arm for reciprocating said second arm to operate said counterweight means to offset torque fluctuations resulting from reciprocation of said folder blade relative to said folder rollers by operation of said first crank assembly.

4. A sheet-folding apparatus as set forth in claim I wherein said counterweight means includes means for statically balancing said blade means and means for reciprocating said blade means to provide static equilibrium of said folding apparatus for positions through which said blade means is moved by said means for reciprocating said blade means during operation of said sheet-folding apparatus.

5. A sheet-folding apparatus as set forth in claim 1 wherein said counterweight means includes a mass which is reciprocated to offset torque fluctuations resulting from reciprocation of said blade means, said mass and blade means being operatively interconnected in such a manner that the acceleration of said mass is substantially zero when said blade means is experiencing its greatest acceleration and the acceleration of said blade means is substantially zero when said mass is experiencing its greatest acceleration.

6. A sheet-handling apparatus comprising a member for engaging sheets, a first crank assembly operatively connected to said member for reciprocating said member to thereby effect movement of the sheets, a mass, a second crank assembly operatively connected to said mass for reciprocating said mass, a shaft operatively interconnecting said first and second crank assemblies, and drive means for rotating said shaft to effect operation of said first and second crank assemblies, said first crank assembly including means for effecting maximum acceleration of said member when said mass is being subjected to substantially zero acceleration by said second crank assembly, said second crank assembly including means for effecting maximum acceleration of said mass when said member is being subjected to substantially zero acceleration by said first crank assembly.

7. A sheet-handling apparatus as set forth in claim 6 wherein said member is mounted on a first arm mounted for pivotal movement under the influence of said first crank assembly, said mass including a second arm mounted for pivotal movement under the influence of said second crank assembly, said first arm being pivoted in a first direction by operation of said first crank assembly to move sheets engaged by said member in said first direction, said first arm being pivoted in a second direction by operation of said first crank assembly to move said member out of engagement with the sheets.

8. A sheet-handling apparatus as set forth in claim 6 wherein said member for engaging the sheets is a folder blade,

said sheet-handling apparatus further including a pair of folder rolls which cooperate to define a nip, said folder blade being movable by operation of said first crank assembly to move the sheets into said nip.

9. A sheet-handling apparatus as set forth in claim 6 wherein said second crank assembly and mass statically balances said first crank assembly and member to provide static equilibrium when said drive means is ineffective to rotate said shaft.

10. A sheet-handling apparatus as set forth in claim 6 wherein said first crank assembly includes means for applying a fluctuating torque load to said shaft upon reciprocation of said member under the influence of said first crank assembly and said second crank assembly includes means for applying to said shaft a fluctuating torque load which is equal and opposite to the fluctuating torque load applied to said shaft by said first crank assembly.

11. A folder assembly for holding sheet material along a predetermined fold line, said folder assembly comprising a pair of cooperating folder rollers defining a nip, conveyor means for transporting sheets of material to a position overlying said nip, a first pivotally mounted arm, a folder blade mounted on said arm, a crankshaft, first crank means for reciprocating said arm to move said blade and sheets toward said nip and then to move said blade away from said nip while the sheets are folded by passing through said nip, said first crank means including a first member fixedly connected to said crankshaft and a first link pivotally connected at one end portion to said first member and at another end portion to said arm whereby rotation of said crankshaft and first member moves said first link to reciprocate said first arm and said blade, a second pivotally mounted arm, second crank means operatively connected to said crankshaft for reciprocating said second arm, said second crank means including a second member fixedly connected to said crankshaft and a second link pivotally connected at one end portion of said second member and at another end portion to said second arm whereby rotation of said crankshaft and said second member moves said second link to reciprocate said second arm, and drive means for rotating said crankshaft to thereby operate said first and second crank means to reciprocate said first and second arms and said blade, said first crank means including means for subjecting said first arm to maximum acceleration when said second arm is being subjected to substantially zero acceleration by operation of said second crank means and said second crank means including means for subjecting said second arm to maximum acceleration when said first arm is being subjected to substantially zero acceleration by operation of said first crank means so that said first and second crank means apply to said crankshaft fluctuating torque loads which offset each other.

12. A folder assembly as set forth in claim 11 wherein said pivot connection between said first link and said first arm is moved along a first path by operation of said first crank means and wherein said pivot connection between said second link and said second arm is moved along a second path extending transversely to said first path by operation of said second crank means.

13. A folder assembly as set forth in claim 11 wherein said first crank means, first arm, and blade are statically balanced by said second crank means and second arm. 

1. A sheet-folding apparatus comprising a pair of folder rollers cooperating to form a nip, means for positioning sheets in a predetermined relationship with said folder rollers, blade means for engaging the sheets and moving them into the nip formed by said folder rollers, means for reciprocating said blade means including a shaft operatively connected with said blade means and drive means for rotating said shaft to effect reciprocation of said blade means, and counterweight means for offsetting torque fluctuation resulting from reciprocation of said blade means, said counterweight means being operatively connected with said shaft whereby rotation of said shaft operates said counterweight means to effect the offsetting of the torque fluctuations resulting from reciprocation of said blade means to thereby tend to minimize torque loading on said shaft during operation of said folding apparatus.
 2. A sheet-folding apparatus as set forth in claim 1 wherein said counterweight means includes a mass which is operatively connected with said shaft and is reciprocated approximately 90* out of phase with reciprocation of said blade means upon rotation of said shaft by said drive means.
 3. A sheet-folding apparatus as set forth in claim 1 wherein said blade means includes a first pivotally mounted arm and a folder blade mounted on said first arm, said means for reciprocating said blade means includes a first crank assembly operatively connected with said shaft and said first arm for reciprocating said first arm to move said folder blade relative to said folder rollers, and said counterweight means includes a second pivotally mounted arm and a second crank assembly operatively connected with said shaft and said second arm for reciprocating said second arm to operate said counterweight means to offset torque fluctuations resulting from reciprocation of said folder blade relative to said folder rollers by operation of said first crank assembly.
 4. A sheet-folding apparatus as set forth in claim 1 wherein said counterweight means includes means for statically balancing said blade means and means for reciprocating said blade means to provide static equilibrium of said folding apparatus for positions through which said blade means is moved by said means for reciprocating said blade means during operation of said sheet-folding apparatus.
 5. A sheet-folding apparatus as set forth in claim 1 wherein said counterweight means includes a mass which is reciprocated to offset torque fluctuations resulting from reciprocation of said blade means, said mass and blade means being operatively interconnected in such a manner that the acceleration of said mass is substantially zero when said blade means is experiencing its greatest acceleration and the acceleration of said blade means is substantially zero when said mass is experiencing its greatest acceleration.
 6. A sheet-handling apparatus comprising a member for engaging sheets, a first crank assembly operatively connected to said member for reciprocating said member to thereby effect movement of the sheets, a mass, a second crank assembly operatively connected to said mass for reciprocating said mass, a shaft operatively interconnecting said first and second crank assemblies, and drive means for rotating said shaft to effect operation of said first and second crank assemblies, said first crank assembly including means for effecting maximum acceleration of said member when said mass is being subjected to substantially zero acceleration by said second crank assembly, said second crank assembly including means for effecting maximum acceleration of said mass when said member is being subjected to substantially zero acceleration by said first crank assembly.
 7. A sheet-handling apparatus as set forth in claim 6 wherein said member is mounted on a first arm mounted for pivotal movement under the influence of said first crank assembly, said mass including a second arm mounted for pivotal movement under the influence of said second crank assembly, said first arm being pivoted in a first direction by operation of said first crank assembly to move sheets engaged by said member in said first direction, said first arm being pivoted in a second direction by operation of said first crank assembly to move said member out of engagement with the sheets.
 8. A sheet-handling apparatus as set forth in claim 6 wherein said member for engaging the sheets is a folder blade, said sheet-handling apparatus further including a pair of folder rolls which cooperate to define a nip, said folder blade being movable by operation of said first crank assembly to move the sheets into said nip.
 9. A sheet-handling apparatus as set forth in claim 6 wherein said second crank assembly and mass statically balances said first crank assembly and member to provide static equilibrium when said drive means is ineffective to rotate said shaft.
 10. A sheet-handling apparatus as set forth in claim 6 wherein said first crank assembly includes means for applying a fluctuating torque load to said shaft upon reciprocation of said member under the influence of said first crank assembly and said second crank assembly includes means for applying to said shaft a fluctuating torque load which is equal and opposite to the fluctuating torque load applied to said shafT by said first crank assembly.
 11. A folder assembly for folding sheet material along a predetermined fold line, said folder assembly comprising a pair of cooperating folder rollers defining a nip, conveyor means for transporting sheets of material to a position overlying said nip, a first pivotally mounted arm, a folder blade mounted on said arm, a crankshaft, first crank means for reciprocating said arm to move said blade and sheets toward said nip and then to move said blade away from said nip while the sheets are folded by passing through said nip, said first crank means including a first member fixedly connected to said crankshaft and a first link pivotally connected at one end portion to said first member and at another end portion to said arm whereby rotation of said crankshaft and first member moves said first link to reciprocate said first arm and said blade, a second pivotally mounted arm, second crank means operatively connected to said crankshaft for reciprocating said second arm, said second crank means including a second member fixedly connected to said crankshaft and a second link pivotally connected at one end portion of said second member and at another end portion to said second arm whereby rotation of said crankshaft and said second member moves said second link to reciprocate said second arm, and drive means for rotating said crankshaft to thereby operate said first and second crank means to reciprocate said first and second arms and said blade, said first crank means including means for subjecting said first arm to maximum acceleration when said second arm is being subjected to substantially zero acceleration by operation of said second crank means and said second crank means including means for subjecting said second arm to maximum acceleration when said first arm is being subjected to substantially zero acceleration by operation of said first crank means so that said first and second crank means apply to said crankshaft fluctuating torque loads which offset each other.
 12. A folder assembly as set forth in claim 11 wherein said pivot connection between said first link and said first arm is moved along a first path by operation of said first crank means and wherein said pivot connection between said second link and said second arm is moved along a second path extending transversely to said first path by operation of said second crank means.
 13. A folder assembly as set forth in claim 11 wherein said first crank means, first arm, and blade are statically balanced by said second crank means and second arm. 